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Theses and Dissertations

Permanent URI for this collectionhttps://hdl.handle.net/10217/199889

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Browsing Theses and Dissertations by Author "Arabi, Mazdak, committee member"

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    Aircraft survivability modeling, evaluation, and optimization for multi-UAV operational scenarios
    (Colorado State University. Libraries, 2021) Lunsford, Ian, author; Bradley, Thomas, advisor; Borky, John, committee member; Shahroudi, Kamran, committee member; Arabi, Mazdak, committee member
    The unmanned aerial vehicle (UAV) has become a prominent aircraft design throughout aerospace applications including commercial, civilian, and military. A UAV is preferred in some missions and applications due to its unique abilities compared to manned aircraft. This dissertation aims to define an improved understanding of the concepts and modeling of aircraft survivability, as applied to UAVs. Traditionally, survivability as a field has defined and considered survivability primarily in the context of manned aircraft, and single aircraft. With UAV's increasing importance in multi-UAV operational scenarios, it has become increasingly important to understand aircraft survivability for singles and groups of UAVs. This research effort has been structured into three research questions defining contributions in survivability modeling, validation, and UAV aircraft design. Research Question 1 seeks to demonstrate the feasibility of a parametric model of UAV survivability. The result is a UAV survivability model and simulation which illustrates key tradeoffs within UAV survivability. The effects on survivability on UAV design characteristics (speed, wing area, drag and lift coefficients) is quantified specific to the detailed lethal envelope simulation method. Research Question 2 aims to verify and validate the UAV survivability simulation, providing evidence of the predictive capability of the survivability simulation results. Evidence is presented for verification and validation through comparison to previous modeling efforts, through solicitation of expert opinion, and through parameter variability and sensitivity analysis. Lastly, Research Question 3 seeks to apply the simulation results to multi-UAV tactical evaluation and single aircraft design. The results illustrate the level of improvement that can be realized through UAV design including armoring (a 25% survivability improvement through 1000kg of armoring), speed increases (a 100 mph increase in cruise speed realizes a 14% decrease in killability), and other relevant design variables. Results also demonstrate that multi-UAV tactics can improve the survivability of UAVs in combat. Loyal wingman tactics are simulated to increase the survivability of a C-130J (equivalent UAV) from 19.8% to 40.0%. Other single UAV tactics such as fuel dumping, afterburners are evaluated under the same framework for their relative effectiveness. This dissertation answers the described research questions by presenting an aircraft survivability evaluation approach that relates survivability with modern UAV applications, emerging threats, multi-UAV tactics, and UAV design. Aircraft survivability encounters with modern UAV countermeasures are considered and simulated. UAV metrics of performance are modeled and simulated to describe aircraft design parameters sensitive to improving aircraft survivability. By evaluating aircraft survivability with a modern multi-UAV tactical perspective, this study seeks to provide the UAV designer with more complete vision of survivability-derived design criteria.
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    Engineering and scaling cement-based carbon storage systems
    (Colorado State University. Libraries, 2024) Winters, Dahl, author; Simske, Steven, advisor; Bradley, Thomas, committee member; Arabi, Mazdak, committee member; Troxell, Wade, committee member; Goemans, Christopher, committee member
    This work is a contribution to the body of knowledge surrounding cement-based carbon storage systems, their engineering, and their scaling to meet the requirements of global sustainability in a relevant timeframe. Concrete is the most produced material by weight per year, surpassing water and all biomass we use per year, thus requiring by virtue of its total mass the largest share of total energy produced. Today, it is a source of net greenhouse gas emissions and environmental damage because of our appropriation of natural resources for its use in construction. However, it could serve as our largest land-based engineered sink for such emissions. Such potential is the focus of this work, addressed not only by experiments to improve the engineering of cement-based carbon storage systems, but also by suggested practices to achieve scale for such systems to have a beneficial impact on our economy and environment. The ubiquity of concrete means that cement-based carbon storage can also be ubiquitous, offering continued opportunities for carbon removal and sequestration within built materials. To engineer and scale the world's largest product into its largest engineered carbon sink, this research focuses on the use of biochar and calcium carbonate within structural and non-structural concrete uses, such as tetrapods: structures offering the benefits of reduced sand mining, protections against sea level rise, and enabling cement industry decarbonization. The results demonstrated that 4 wt% biochar with 1.5 wt% CaCO3 can replace cement for carbon storage while maintaining sufficient compressive strength. Along with the use of 30 wt% biochar as aggregate, 100,000 10-tonne tetrapods could sequester 1 million tonnes of CO2. Over a year of global emissions, 40 Gt CO2, could be stored in such stacked tetrapods within a land area smaller than Kuwait, 17,400 km2. Thus, this work contributes to the engineering of systems with industrial significance capable of countering the effects of global warming at meaningful scales.